IIS7 Rewrite-URL block everything except one URL


19+ years progress programming and still learning.
I know this question is outside the scope of this forum but you guys are just great.

So I have a WebSpeed Messenger running on IIS7. WebSpeed being used for XML HTTP API and not the traditional web pages which included images/css/js etc.

I'm using the Rewrite-URL module so I can have a nice pretty simple looking URL and not have all that nasty scripts/cgiip.exe/WService=foobar stuff, this is what I already have working.

So, how can I use the Rewrite-URL module under IIS7 to block every URL request except the one I want?